The present invention relates to a method and/or architecture for implementing wide dynamic range amplifiers generally and, more particularly, to a method and/or architecture for implementing transimpedance amplifiers with improved linearity and dynamic range that may be used in broadband telecom and datacom applications.
Wide dynamic range amplifiers are widely employed in the wireless and wireline industry. Conventional transimpedance amplifiers used in fiber optic systems must receive photo-diode currents ranging from as low as a few micro-amps to as high as a few milli-amps, while maintaining low duty-cycle distortion and minimal intersymbol interference (ISI). Conventional approaches for improving linearity and dynamic range, especially when encountering high incident input powers, include [1] automatic gain control field effect transistor (FET) amplifiers (e.g., U.S. Pat. No. 5,646,573); [2] common-base inputs stage amplifiers (e.g., Integrated High Frequency Low Noise Current Mode Optical Transimpedance Preamplifier: Theory and Practice, IEEE JSSC, June 1995, pp. 667); [3] complementary common-base input amplifiers (e.g., U.S. Pat. No. 6,069,534); and [4] differential common-base amplifiers with current switch inputs (e.g., Wide-Band Integrated Optical Receiver with Improved Dynamic Range Using a Current Switch at the Input, IEEE JSSC, Vol. 28, No. 7, July 1991, pp. 862-864), all of which are hereby incorporated by reference in their entirety.
Additionally, providing a monitor current which is linearly proportional to a received optical power is difficult. Providing a linearly proportional monitoring current is challenging due to nonlinear transimpedance gain when high incident powers and/or automatic gain control means are employed.
It would be desirable to provide a microwave monolithic integrated circuit (MMIC) amplifier which can amplify a large input signal while minimizing signal distortion. Such an amplifier is coveted by engineers who are trying to build superior radio frequency (RF) and fiber-optic receiver systems.
The present invention concerns an apparatus comprising an amplifier circuit and a control circuit. The amplifier circuit may be configured to generate an amplified signal in response to an input signal. The control circuit generally comprises a differential amplifier having (i) a first input coupled to said amplified signal and (ii) a second input coupled to a reference voltage. The control circuit may be configured to control a dynamic range of the amplifier circuit by adjusting the input signal based on (i) a loop gain of the control circuit and (ii) the reference voltage.
The objects, features and advantages of the present invention include providing a method and/or architecture for implementing amplifiers with improved linearity and dynamic range that may (i) provide wide dynamic range in a low noise amplifier; (ii) be implemented in wireless RF applications; (iii) be implemented in a transimpedance amplifier for fiber-optic applications; (iv) be implemented without sacrificing the low noise input sensitivity of conventional amplifiers; and/or (v) be used in broadband telecom and datacom applications.